Figure 2.

Schematic representation of the distribution and maturation of microglia and the beginning of astrogenesis in the mouse cerebral cortex. (A) At early embryonic stages between E8 and E12, microglia are located at the PS in the meninges and in the lateral ventricles. Only a few highly, motile and proliferative cells can be found in the neuroepithelium. (B) Between E14 and E16, microglia ramify further to form intermediate ramified microglia that can be found in the VZ, SVZ, IZ, SP and MZ. At the PS and in the lateral ventricle, one can still detect amoeboid microglia. Remarkably, until E16, microglia are absent from the cortical plate. (C) From E18 and onwards, microglia can be found in the cortical layers, after migrating from the deeper to the more superficial layers. During this period, microglia are found in close association with radial glia, blood vessels and developing axons. Around E18 astrogenesis starts. Similar to microglia, astrocytes are also found near radial glia, blood vessels and axons. Along the course of embryonic brain development, many microglia ramify further and transform from intermediate ramified microglia into mature ramified microglia with long processes. Abbreviations: PS, pial surface; N, neuroepithelium; MZ, marginal zone; CP, cortical plate; SP, subplate; IZ, intermediate zone; SVZ, subventricular zone; VZ, ventricular zone; P, parenchyma.